1. Field of the Invention
The present invention relates, generally, to spectral interleavers and, in preferred embodiments, to devices and methods for producing athermal birefringent optical interleavers with flat-top passbands.
2. Description of Related Art
Spectral interleavers are important devices for applications in Dense Wavelength Division Multiplexing (DWDM) optical communication networks. Conventional interleavers are made of optical interferometers which employ a beam splitter (BS) to split the input beam in two. These two beams are then recombined at the beam splitter using two mirrors to provide the retro-reflection. The interferometers can be Michelson interferometers, Mach-Zehnder interferometers, or birefringent interferometers. When a path length difference exists between the two interfering beams, these conventional interleavers provide a sinusoidal spectral transmission function. Under the appropriate conditions, the transmission maxima and minima can be tuned to match the International Telecommunications Union (ITU) frequency channels. Thus, such interferometers can be employed as spectral interleavers for DWDM applications. An interleaver can separate a set of multiplexed frequency channels into two subsets with mutually interleaving frequency channels in each set. However, when a significant signal bandwidth exists in each of the channels, the sinusoidal transmission function can lead to signal loss and distortion. A desirable interleaver should provide a flat top spectral transmission passband for each of the ITU frequency channels.
However, the performance of most conventional interleavers is either inadequate in terms of passband flatness and stopband isolation, or sensitive to external temperature change.